1. Technical Field
The present invention relates to an organic transistor manufactured using a liquid semiconductor material and a method for manufacturing the organic transistor.
2. Related Art
Organic semiconductors have lower intermolecular binding energies than inorganic semiconductors, and accordingly can form films in low-energy processes. In particular, a solution of an organic semiconductor material in a solvent can be used for forming a semiconductor element by a known printing technique, such as an ink jet method, and the process using such an organic semiconductor material solution has received attention as a new low-energy, low-cost, high-throughput semiconductor process. For example, JP-A-2009-72654 discloses that a film pattern of a semiconductor device is formed by an ink jet method. JP-A-2005-217359 discloses another semiconductor process using a liquid material. In this process, an insulating film is partially dissolved by being coated with a liquid material containing a solvent, and the solute in the liquid material forms another electroconductive film.
While the substrates of transistors and ICs are typically made of silicon or glass, processes for forming a transistor using a flexible plastic substrate (made of, for example, polyimide, polyethylene naphthalate or polyethylene terephthalate), an organic semiconductor material, a conductive macromolecular material or an insulating macromolecular material has been studied to achieve a flexible semiconductor device.
Some of the plastics and macromolecular materials contain polar functional groups. If a material having a polar functional group is present in the vicinity of the transistor channel, the characteristics of the transistor may be affected by the polar group. Particularly when the gate insulating layer or the substrate adjacent to the channel of the transistor contains a material (polar material) having a polar functional group, the characteristics (threshold voltage, off current, etc.) are liable to be affected by the polar group. Even if the gate insulating layer is made of a non-macromolecular material, such as silicon oxide, the gate insulating layer contains polar molecules having a polar group, such as hydroxy group —OH, which has penetrated from the atmosphere used in the process. The characteristics of the transistor are affected by polar molecules or a polar substance present in the vicinity of the channel.